Many modern electronic systems incorporate various modular electronic components. For example, personal computers may include modular electronic components in the form of dynamic random access memory units. Each of the modular electronic components may include an integrated circuit fabricated on a semiconductor substrate. Each modular electronic component may be coupled to the electronic system by a series of pins extending in a predetermined sequence from a body of the modular electronic component. The pins may be coupled to leads of a leadframe and external leads or balls may be coupled to the electronic system.
As the density of devices on integrated circuits has continued to increase, the number of leads and traces required for an integrated chip have also increased. At the same time, the size of the integrated circuit chips has in many instances decreased. To help handle the increased density and smaller size, ball grid arrays ("BGA's") were developed.
A ball grid array is a type of package for integrated circuits in which one or more integrated circuit chips are mounted on a top substrate surface, and electrical connection is made to an electrically conductive material, such as the printed circuit board, by an array of small solder balls located on the surface of the substrate opposite from the integrated circuit chip. Traces on the chip side of the substrate may be electrically connected to the solder balls by through-holes which have been electrically plated.
A number of difficulties may be experienced with BGAs because of the different coefficients of thermal expansion of the various components. This and high stresses in some areas have caused some of the solder balls to crack and display other problems. Furthermore, a typical BGA operation requires extreme care in locating and attaching the solder balls to the plating of the through-holes on the side of the substrate opposite the chip. To help alleviate some of the problems with the solder balls cracking and high stress areas, an underfill is sometimes placed around the solder balls and between them. Positioning the underfill around the solder balls, however, presents an extra process step and may involve a difficult operation.